Influence of the knee flexion on muscle activation and transmissibility during whole body vibration

The influence of the knee flexion on muscle activation and transmissibility during whole body vibration is controversially discussed in the literature. In this study, 34 individuals had electromyography activity (EMG) of the vastus lateralis and the acceleration assessed while squatting with 60° and 90° of knee flexion either with or without whole-body vibration (WBV). The conditions were maintained for 10 s with 1 min of rest between each condition. The main findings were (1) the larger the angle of knee flexion (90° vs. 60°), the greater the EMG (p < 0.001), with no difference on acceleration transmissibility; (2) for both angles of knee flexion, the addition of WBV produced no significant difference in EMG and higher acceleration compared to without WBV (p < 0.001). These results suggest that the larger the knee flexion angle (60° vs. 90°), the greater the muscle activation without acceleration modification. However, the addition of WBV increases the transmissibility of acceleration in the lower limbs without modification in EMG of vastus lateralis.     

Effects of whole body vibration on motor unit recruitment and threshold

Whole body vibration (WBV) has been suggested to elicit reflex muscle contractions but this has never been verified. We recorded from 32 single motor units (MU) in the vastus lateralis of 7 healthy subjects (34 ± 15.4 yr) during five 1-min bouts of WBV (30 Hz, 3 mm peak to peak), and the vibration waveform was also recorded. Recruitment thresholds were recorded from 38 MUs before and after WBV. The phase angle distribution of all MUs during WBV was nonuniform (P < 0.001) and displayed a prominent peak phase angle of firing. There was a strong linear relationship (r = -0.68, P < 0.001) between the change in recruitment threshold after WBV and average recruitment threshold; the lowest threshold MUs increased recruitment threshold (P = 0.008) while reductions were observed in the higher threshold units (P = 0.031). We investigated one possible cause of changed thresholds. Presynaptic inhibition in the soleus was measured in 8 healthy subjects (29 ± 4.6 yr). A total of 30 H-reflexes (stimulation intensity 30% Mmax) were recorded before and after WBV: 15 conditioned by prior stimulation (60 ms) of the antagonist and 15 unconditioned. There were no significant changes in the relationship between the conditioned and unconditioned responses. The consistent phase angle at which each MU fired during WBV indicates the presence of reflex muscle activity similar to the tonic vibration reflex. The varying response in high- and low-threshold MUs may be due to the different contributions of the mono- and polysynaptic pathways but not presynaptic inhibition.     

Acute bone response to whole body vibration in healthy pre-pubertal boys

The skeleton responds to mechanical stimulation. We wished to ascertain the magnitude and speed of the growing skeleton’s response to a standardised form of mechanical stimulation, vibration. 36 prepubertal boys stood for 10 minutes in total on one of two vibrating platforms (high (>2 g) or low (<1 g) magnitude vibration) on either 1, 3 or 5 successive days (n=12 for each duration); 15 control subjects stood on an inactive platform. Blood samples were taken at intervals before and after vibration to measure bone formation (P1NP, osteocalcin) and resorption (CTx) markers as well as osteoprotegerin and sclerostin. There were no significant differences between platform and control groups in bone turnover markers immediately after vibration on days 1, 3 and 5. Combining platform groups, at day 8 P1NP increased by 25.1% (CI 12.3 to 38.0; paired t-test p=0.005) and bone resorption increased by 10.9% (CI 3.6 to 18.2; paired t-test p=0.009) compared to baseline. Osteocalcin, osteoprotogerin and sclerostin did not change significantly. The growing skeleton can respond quickly to vibration of either high or low magnitude. Further work is needed to determine the utility of such “stimulation-testing” in clinical practice.     

Effect of whole body vibration frequency on neuromuscular activity in ACL-deficient and healthy males

Whole-body vibration (WBV) has been shown to enhance muscle activity via reflex pathways, thus having the potential to contrast muscle weakness in individuals with rupture of the anterior cruciate ligament (ACL). The present study aimed to compare the magnitude of neuromuscular activation during WBV over a frequency spectrum from 20 to 45 Hz between ACL-deficient and healthy individuals. Fifteen males aged 28±4 with ACL rupture and 15 age-matched healthy males were recruited. Root mean square (RMS) of the surface electromyogram from the vastus lateralis in both limbs was computed during WBV in a static half-squat position at 20, 25, 30, 35, 40 and 45 Hz, and normalized to the RMS while maintaining the half-squat position without vibration. The RMS of the vastus lateralis in the ACL-deficient limb was significantly greater than in the contralateral limb at 25, 30, 35 and 40 Hz (P<0.05) and in both limbs of the healthy participants (dominant limb at 25, 30, 35, 40 and 45 Hz, P<0.05; non dominant limb at 20, 25, 30, 35, 40 and 45 Hz, P<0.05). The greater neuromuscular activity in the injured limb compared to the uninjured limb of the ACL-deficient patients and to both limbs of the healthy participants during WBV might be due to either augmented excitatory or reduced inhibitory neural inflow to motoneurons of the vastus lateralis through the reflex pathways activated by vibratory stimuli. The study provides optimal WBV frequencies which might be used as reference values for ACL-deficient patients.     

Preliminary results on the mobility after whole body vibration in immobilized children and adolescents

The present article is a preliminary report on the effect of Whole Body Vibration (WBV) on the mobility in long-term immobilized children and adolescents. WBV was applied to 6 children and adolescents (diagnoses: osteogenesis imperfecta, N=4; cerebral palsy, N=1; dysraphic defect of the lumbar spine, N=1) over a time period of 6 months. WBV was applied by a vibrating platform constructed on a tilt-table. The treatment effect was measured by alternations of the tilt-angle of the table and with the "Brief assessment of motor function" (BAMF). All 6 individuals were characterized by an improved mobility, which was documented by an increased tilt-angle or an improved BAMF-score. The authors concluded WBV might be a promising approach to improve mobility in severely motor-impaired children and adolescents. Therefore, the Cologne Standing-and-Walking- Trainer powered by Galileo is a suitable therapeutic device to apply WBV in immobilized children and adolescents.     

The influence of whole body vibration on the plantarflexors during heel raise exercise

Whole body vibration (WBV) during exercise offers potential to augment the effects of basic exercises. However, to date there is limited information on the basic physiological and biomechanical effects of WBV on skeletal muscles. The aim of this study was to determine the effects of WBV (40 Hz, 1.9 mm synchronous vertical displacement) on the myoelectrical activity of selected plantarflexors during heel raise exercise. 3D motion capture of the ankle, synchronised with sEMG of the lateral gastrocnemius and soleus, was obtained during repetitive heel raises carried out at 0.5 Hz on 10 healthy male subjects (age 27 ± 5 years, height 1.78 ± 0.04 m, weight 75.75 ± 11.9 kg). During both vibration and non vibration the soleus activation peaked earlier than that of the lateral gastrocnemius. The results indicate that WBV has no effect on the timing of exercise completion or the amplitude of the lateral gastrocnemius activity, however significant increases in amplitudes of the soleus muscle activity (77.5–90.4% MVC P < 0.05). WBV had no significant effect on median frequencies of either muscle. The results indicate that the greatest effect of WBV during heel raise activity is in the soleus muscles during the early phases of heel raise.     

Spectrum analysis of stabilograms with special reference to changes following whole body vibration

The location of the body's gravicenter in the horizontal plane was measured by means of a force platform. The 4 male subjects stood upright with eyes closed. Power-density spectra of the frontal and sagittal stabilograms were estimated. Repeated investigations made it possible to assess intraindividual variability and to evaluate significant interindividual differences. The power spectral density was not altered by a controlled sitting posture observed for 30 min. Low-frequency whole-body vibration with an exposure time of 30 min and a permissible level according to the "fatigue decreased proficiency boundary" (International Standard ISO 2631) induced a significant increase of the power spectral density below 0.25 Hz and a decrease above this frequency. The results indicate that the power density spectral analysis of stabilograms is a suitable method for evaluating a biological effect of vibration.     

Seated whole body vibrations with high-magnitude accelerations--relative roles of inertia and muscle forces

Reliable computation of spinal loads and trunk stability under whole body vibrations with high acceleration contents requires accurate estimation of trunk muscle activities that are often overlooked in existing biodynamic models. A finite element model of the spine that accounts for nonlinear load- and direction-dependent properties of lumbar segments, complex geometry and musculature of the spine, and dynamic characteristics of the trunk was used in our iterative kinematics-driven approach to predict trunk biodynamics in measured vehicle's seat vibrations with shock contents of about 4g (g: gravity acceleration of 9.8m/s(2)) at frequencies of about 4 and 20Hz. Muscle forces, spinal loads and trunk stability were evaluated for two lumbar postures (erect and flexed) with and without coactivity in abdominal muscles. Estimated peak spinal loads were substantially larger under 4Hz excitation frequency as compared to 20Hz with the contribution of muscle forces exceeding that of inertial forces. Flattening of the lumbar lordosis from an erect to a flexed posture and antagonistic coactivity in abdominal muscles, both noticeably increased forces on the spine while substantially improving trunk stability. Our predictions clearly demonstrated the significant role of muscles in trunk biodynamics and associated risk of back injuries. High-magnitude accelerations in seat vibration, especially at near-resonant frequency, expose the vertebral column to large forces and high risk of injury by significantly increasing muscle activities in response to equilibrium and stability demands.     

Whole-body vibration increases upper and lower body muscle activity in older adults: potential use of vibration accessories

The current study examined the effects of whole-body vibration (WBV) on upper and lower body muscle activity during static muscle contractions (squat and bicep curls). The use of WBV accessories such as hand straps attached to the platform and a soft surface mat were also evaluated. Surface electromyography (sEMG) was measured for the medial gastrocnemius (MG), vastus lateralis (VL), and biceps brachii (BB) muscles in fourteen healthy older adults (74.8±4.5 years; mean±SD) with a WBV stimulus at an acceleration of 40 m s(-2) (30 Hz High, 2.5 mm or 46 Hz Low, 1.1 mm). WBV increased lower body (VL and MG) sEMG vs baseline (no WBV) though this was decreased with the use of the soft mat. The addition of the bicep curl with hand straps had no effect on lower body sEMG. WBV also increased BB sEMG vs baseline which was further increased when using the hand straps. There was no upper body effect of the soft mat. This study demonstrates WBV increases both lower and upper body muscle activity in healthy older adults. Moreover, WBV accessories such as hand straps attached to the platform or a soft surface mat may be used to alter exercise intensity.     

Obese adolescents exhibit a constant ratio of GH isoforms after whole body vibration and maximal voluntary contractions

Background

Growth hormone (GH) is a heterogeneous protein composed of several molecular isoforms, the most abundant ones being the 22?kDa- and 20?kDa-GH. Exercise-induced secretion of GH isoforms has been extensively investigated in normal-weight individuals due to antidoping purposes, particularly recombinant human GH (rhGH) abuse. On the other hand, the evaluation of exercise-induced responses in GH isoforms has never been performed in obese subjects.

Methods

The acute effects of whole body vibration (WBV) or maximal voluntary contraction (MVC) alone and the combination of MVC with WBV (MVC?+?WBV) on circulating levels of 22?kDa- and 20?kDa-GH were evaluated in 8 obese male adolescents [mean age?±?SD: 17.1?±?3.3?yrs.; weight: 107.4?±?17.8?kg; body mass index (BMI): 36.5?±?6.6?kg/m²; BMI standard deviation score (SDS): 3.1?±?0.6].

Results

MVC (alone or combined with WBV) significantly stimulated 22?kDa- and 20?kDa-GH secretion, while WBV alone was ineffective. In particular, 22?kDa- and 20?kDa-GH peaks were significantly higher after MVC?+?WBV and MVC than WBV. In addition, 22?kDa-GH (but not 20?kDa-GH) peak was significantly higher after MVC?+?WBV than MVC. Importantly, the ratio of circulating levels of 22?kDa- to 20?kDa-GH was constant throughout the time window of evaluation after exercise and similar among the three different protocols of exercise.

Conclusions

The results of the present study confirm the ability of MVC, alone and in combination with WBV, to stimulate both 22?kDa- and 20?kDa-GH secretion in obese patients, these responses being related to the exercise workload. Since the ratio of 22?kDa- to 20?kDa-GH is constant after exercise and independent from the protocols of exercise as in normal-weight subjects, hyposomatotropism in obesity does not seem to depend on an unbalance of circulating GH isoforms. Since the present study was carried out in a small cohort of obese sedentary adolescents, these preliminary results should be confirmed in further future studies enrolling overweight/obese subjects with a wider age range.

     

Relevance of motion artifact in electromyography recordings during vibration treatment

Electromyography readings (EMGs) from quadriceps of fifteen subjects were recorded during whole body vibration treatment at different frequencies (10–50 Hz). Additional electrodes were placed on the patella to monitor the occurrence of motion artifact, triaxial accelerometers were placed onto quadriceps to monitor motion. Signal spectra revealed sharp peaks corresponding to vibration frequency and its harmonics, in accordance with the accelerometer data. EMG total power was compared to that associated with vibration harmonics narrow bands, before and during vibration. On average, vibration associated power resulted in only 3% (±0.9%) of the total power prior to vibration and 29% (±13.4%) during vibration. Often, studies employ surface EMG to quantitatively evaluate vibration evoked muscular activity and to set stimulation frequency. However, previous research has not accounted for motion artifacts. The data presented in this study emphasize the need for the removal of motion artifacts, as they consistently affect RMS estimation, which is often used as a concise muscle activity index during vibrations. Such artifacts, rather unpredictable in amplitude, might be the cause of large inter-study differences and must be eliminated before analysis. Motion artifact filtering will contribute to thorough and precise interpretation of neuromuscular response to vibration treatment.     

Associations between the masticatory system and muscle activity of other body districts. A meta-analysis of surface electromyography studies

The aim of this meta-analysis regarding the use of surface electromyography (sEMG) is to assess the scientific evidence for detectable correlations between the masticatory system and muscle activity of the other body districts, particularly those mainly responsible for body posture. A literature survey was performed using the PubMed database, covering the period from January 1966 to April 2011, and choosing medical subject headings. After selection, five articles qualified for the final analysis. One study article was judged to be of medium quality, the remaining four of low quality. No study included a control group or follow-up; in only one study, subjects with impairment of the masticatory system were enrolled. In all studies, detectable correlations between the masticatory systems and muscle activity of the other body districts, or vice versa, were found; however, after a reappraisal of the data provided in these studies, only weak correlations were found, which reached biological, but not clinical relevance. With the limitations that arise from the poor methodological quality of the published study reports discussed here, the conclusion is that a correlation between the masticatory system and muscle activity of the other body districts might be detected through sEMG under experimental conditions; however, this correlation has little clinical relevance. While more investigations with improved levels of scientific evidence are needed, the current evidence does not support clinically relevant correlations between the masticatory system and the muscle activity of other body districts, including those responsible for body posture.     

Reliability of leg muscle electromyography in vertical jumping

In this study we aimed to determine the reliability of the surface electromyography (EMG) of leg muscles during vertical jumping between two test sessions, held 2 weeks apart. Fifteen females performed three maximal vertical jumps with countermovement. The displacement of the body centre of mass (BCM), duration of propulsion phase (time), range of motion (ROM) and angular velocity of the knee and surface EMG of four leg muscles (rectus femoris, vastus medialis. biceps femoris and gastrocnemius) were recorded during the jumps. All variables were analysed throughout the propulsion and mid-propulsion phases. Intraclass correlation coefficients (ICC) for the rectus femoris, vastus medialis, biceps femoris and gastrocnemius were calculated to be 0.88, 0.70, 0.24 and 0.01, respectively. BCM, ROM and time values all indicated ICC values greater than 0.90, and the mean knee angular velocity was slightly lower, at 0.75. ICCs between displacement of the BCM and integrated EMG (IEMG) of the muscles studied were less than 0.50. The angular velocity of the knee did not correlate well with muscle activity. Factors that may have affected reliability were variations in the position of electrode replacement, skin resistance, cross-talk between muscles and jump mechanics. The results of this study suggest that while kinematic variables are reproducible over successive vertical jumps, the degree of repeatability of an IEMG signal is dependent upon the muscle studied.     

Enhancement of whole body glucose uptake during and after human skeletal muscle low-frequency electrical stimulation.

There is considerable evidence to suggest that electrical stimulation (ES) activates glucose uptake in rodent skeletal muscle. It is, however, unknown whether ES can lead to similar metabolic enhancement in humans. We employed low-frequency ES through surface electrodes placed over motor points of quadriceps femoris muscles. In male subjects lying in the supine position, the highest oxygen uptake was obtained by a stimulation pattern with 0.2-ms biphasic square pulses at 20 Hz and a 1-s on-off duty cycle. Oxygen uptake was increased by approximately twofold throughout the 20-min stimulation period and returned to baseline immediately after stimulation. Concurrent elevation of the respiratory exchange ratio and blood lactate concentration indicated anaerobic glycogen breakdown and utilization during ES. Whole body glucose uptake determined by the glucose disposal rate during euglycemic clamp was acutely increased by 2.5 mg. kg(-1). min(-1) in response to ES and, moreover, remained elevated by 3-4 mg. kg(-1). min(-1) for at least 90 min after cessation of stimulation. Thus the stimulatory effect of ES on whole body glucose uptake persisted not only during, but also after, stimulation. Low-frequency ES may become a useful therapeutic approach to activate energy and glucose metabolism in humans.     

Contributions of working muscle to whole body lipid metabolism are altered by exercise intensity and training

To evaluate the contribution of working muscle to whole body lipid oxidation, we examined the effects of exercise intensity and endurance training (9 wk, 5 days/wk, 1 h, 75% Vo(2 peak)) on whole body and leg free fatty acid (FFA) kinetics in eight male subjects (26 +/- 1 yr, means +/- SE). Two pretraining trials [45 and 65% Vo(2 max) (45UT, 65UT)] and two posttraining trials [65% of pretraining Vo(2 peak) (ABT), and 65% of posttraining Vo(2 peak) (RLT)] were performed using [1-(13)C]palmitate infusion and femoral arteriovenous sampling. Training increased Vo(2 peak) by 15% (45.2 +/- 1.2 to 52.0 +/- 1.8 ml.kg(-1).min(-1), P < 0.05). Muscle FFA fractional extraction was lower during exercise (EX) compared with rest regardless of workload or training status ( approximately 20 vs. 48%, P < 0.05). Two-leg net FFA balance increased from net release at rest ( approximately -36 micromol/min) to net uptake during EX for 45UT (179 +/- 75), ABT (236 +/- 63), and RLT (136 +/- 110) (P < 0.05), but not 65UT (51 +/- 127). Leg FFA tracer measured uptake was higher during EX than rest for all trials and greater during posttraining in RLT (716 +/- 173 micromol/min) compared with pretraining (45UT 450 +/- 80, 65UT 461 +/- 72, P < 0.05). Leg muscle lipid oxidation increased with training in ABT (730 +/- 163 micromol/min) vs. 65UT (187 +/- 94, P < 0.05). Leg muscle lipid oxidation represented approximately 62 and 30% of whole body lipid oxidation at lower and higher relative intensities, respectively. In summary, training can increase working muscle tracer measured FFA uptake and lipid oxidation for a given power output, but both before and after training the association between whole body and leg lipid metabolism is reduced as exercise intensity increases.     

Acute effect of whole body vibration on isometric strength,squat jump,and flexibility in well-trained combat athletes

The purpose of this study was to investigate the effect of whole body vibration (WBV) training on maximal strength, squat jump, and flexibility of well-trained combat athletes. Twelve female and 8 male combat athletes (age: 22.8 ± 3.1 years, mass: 65.4 ± 10.7 kg, height: 168.8 ± 8.8 cm, training experience: 11.6 ± 4.7 years, training volume: 9.3 ± 2.8 hours/week) participated in this study. The study consisted of three sessions separated by 48 hours. The first session was conducted for familiarization. In the subsequent two sessions, participants performed WBV or sham intervention in a randomized, balanced order. During WBV intervention, four isometric exercises were performed (26 Hz, 4 mm). During the sham intervention, participants performed the same WBV intervention without vibration treatment (0 Hz, 0 mm). Hand grip, squat jump, trunk flexion, and isometric leg strength tests were performed after each intervention. The results of a two-factor (pre-post[2] × intervention[2]) repeated measures ANOVA revealed a significant interaction (p = 0.018) of pre-post × intervention only for the hand grip test, indicating a significant performance increase of moderate effect (net increase of 2.48%, d = 0.61) after WBV intervention. Squat jump, trunk flexion, and isometric leg strength performances were not affected by WBV. In conclusion, the WBV protocol used in this study potentiated hand grip performance, but did not enhance squat jump, trunk flexion, or isometric leg strength in well-trained combat athletes.     

Trunk muscle activity during stability ball and free weight exercises

The purpose of this investigation was to compare trunk muscle activity during stability ball and free weight exercises. Nine resistance-trained men participated in one testing session in which squats (SQ) and deadlifts (DL) were completed with loads of approximately 50, 70, 90, and 100% of one-repetition maximum (1RM). Isometric contractions during 3 stability ball exercises (quadruped (QP), pelvic thrust (PT), ball back extension (BE)) were also completed. During all exercises, average integrated electromyography (IEMG) from the rectus abdominus (RA), external oblique (EO), longissimus (L1) and multifidus (L5) was collected and analyzed. Results demonstrate that when expressed relative to 100% DL 1RM, muscle activity was 19.5 +/- 14.8% for L1 and 30.2 +/- 19.3% for L5 during QP, 31.4 +/- 13.4% for L1 and 37.6 +/- 12.4% for L5 during PT, and 44.2 +/- 22.8% for L1 and 45.5 +/- 21.6% for L5 during BE. IEMG of L1 during SQ and DL at 90 and 100% 1RM, and relative muscle activity of L5 during SQ and DL at 100% 1RM was significantly greater (P < or = 0.05) than in the stability ball exercises. Furthermore, relative muscle activity of L1 during DL at 50 and 70% 1RM was significantly greater than in QP and PT. No significant differences were observed in RA and EO during any of the exercises. In conclusion, activity of the trunk muscles during SQs and DLs is greater or equal to that which is produced during the stability ball exercises. It appears that stability ball exercises may not provide a sufficient stimulus for increasing muscular strength or hypertrophy; consequently, the role of stability ball exercises in strength and conditioning programs is questioned. SQs and DLs are recommended for increasing strength and hypertrophy of the back extensors.     

Sensitivity analysis of an energetic muscle model applied at whole body level in recumbent pedalling

Musculoskeletal models are used in order to describe and analyse the mechanics of human movement. In order to get a complete evaluation of the human movement, energetic muscle models were developed and were shown to be promising. The aim of this work is to determine the sensitivity of muscle mechanical and energetic model estimates to changes in parameters during recumbent pedalling. Inputs of the model were electromyography and joint angles, collected experimentally on one participant. The sensitivity analysis was performed on muscle-specific tension, physiological cross-sectional area, muscle maximal force, tendon rest length and percentage of fast-twitch fibres using an integrated sensitivity ratio. Soleus, gastrocnemius, vasti, gluteus and medial hamstrings were selected for the analyses. The energetic model was found to be always less sensitive to parameter changes than the mechanical model. Tendon slack length was found to be the most critical parameter for both energetic and mechanical models even if the effect on the energetic output was smaller than on muscle force and joint moments.     

Trunk muscle activation during golf swing: Baseline and threshold

There is a lack of studies regarding EMG temporal analysis during dynamic and complex motor tasks, such as golf swing. The aim of this study is to analyze the EMG onset during the golf swing, by comparing two different threshold methods. Method A threshold was determined using the baseline activity recorded between two maximum voluntary contraction (MVC). Method B threshold was calculated using the mean EMG activity for 1000 ms before the 500 ms prior to the start of the Backswing. Two different clubs were also studied. Three-way repeated measures ANOVA was used to compare methods, muscles and clubs. Two-way mixed Intraclass Correlation Coefficient (ICC) with absolute agreement was used to determine the methods reliability.Club type usage showed no influence in onset detection. Rectus abdominis (RA) showed the higher agreement between methods. Erector spinae (ES), on the other hand, showed a very low agreement, that might be related to postural activity before the swing. External oblique (EO) is the first being activated, at 1295 ms prior impact. There is a similar activation time between right and left muscles sides, although the right EO showed better agreement between methods than left side. Therefore, the algorithms usage is task- and muscle-dependent.